This invention is directed to an autofocus system for focusing a camera, and in particular to such a system for use on studio television cameras.
A typical television camera now in general usage by television stations in their studios is shown in FIG. 1. The main constituents of camera 1 are lens 3, camera body 5 and monitor 7. Camera body 5 houses the sensors responsive to the image viewed through lens 3, as well as the necessary electronics to generate the electrical signals which are eventually transmitted to the public viewing audience. Monitor 7 which is mounted atop (as shown) or incorporated within (not shown) camera body 5, is a standard television set with a 5 inch screen 8 which displays the scene viewed through lens 3. It is, of course, suitably connected to camera body 5 which provides it with the signals required to produce the displayed image. The cameraman places his forehead against hood, or visor, 10 and peers at this monitor to aim and focus the camera. He aims it by maneuvering the camera until the scene of interest comes on screen 8. The cameraman focuses the camera by manually turning a focusing wheel (not shown) linked to the lens and which controls its setting. Hood 10 serves to shade screen 8 from the bright lights in the studio so that the displayed image is not washed out.
One problem with the just-described system lies in the manual focusing method. In order to minimize the manual focusing required as the camera is shifted in position from one scene to another, the studio must be bathed in intensely bright light to maximize the depth of field. This type of lighting also softens any focusing errors so they are not noticeable. However, such lighting conditions are uncomfortable because of the concomitant heat generated as well as the visual discomfort caused to people with sensitive eyes. Also, the need to focus manually in conditions of quickly shifting scenes puts a burden on the cameraman's capacity to operate the camera properly.
Despite the benefits of automating the focusing function, such as freeing the cameraman from that chore so he can better concentrate on other matters, only the small consumer-type cameras have been supplied with an autofocus system. The larger, more sophisticated cameras such as studio television cameras do not have this feature. It is felt this may be due to the relatively wide focusing field of view, such as 20 degrees, of such autofocus devices. An autofocus system will tend to focus on the most prominent object in its field of view. Since the field of view is so wide, it is likely in many instances that a misfocus will occur because the object of interest is not the one most prominent. Thus, despite its apparent advantages, an autofocus system in this environment is not practical.